In Vivo Release from Cerebral Cortex of [14C]Glutamate Synthesized from [U‐14C]Glutamine

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Abstract
Awake, unrestrained and behaviorally normal [rats] with superfusion cannulae implanted over the sensorimotor cortex were used in a study of the capacity of infused [U-14C]glutamine for labeling glutamate and other amino acids released by depolarizing stimuli. A spontaneous background release of [14C]glutamate was detected. This was increased by tityustoxin (1 .mu.M). The specific radioactivity of glutamate increased 8-fold during the evoked-release period. [14C]Aspartate was also detected and showed increased release, but not increased specific labeling, in response to depolarization. Evoked GABA release occurred but only small amounts of [14C]GABA were detected. Glutamine showed increased rates of uptake to the sensorimotor cortex during stimulation periods, suggesting an accelerated breakdown via glutaminase.